Bay-substituted Perylene diimides (PDIs) as redox mediators in dye-sensitized solar cells and active electrode material in supercapacitors

In recent years, innovations in materials design have improved the optoelectronic properties of advanced materials and facilitated their efficient utilization. A significant amount of research has been conducted on developing perylene diimide (PDI) dyes for their use in various energy-related applications. In the present work, we have synthesized bay-substituted PDI derivatives and explored their dual applications in energy harvesting and storage devices. The nucleophilic substitution reaction of 1,7/1,6-brominated Val-PDI was performed by using 2-naphthol (N) and its Nitrogen analogue 8-hydroxy quinoline (Q) for analysing the effect of N-heterocycle at the bay position. The prepared 1,7 (N1/Q1) and 1,6 (N2/Q2) PDIs underwent thorough photophysical and electrochemical analyses and their structures were optimized through density functional theory (DFT) using B3LYP approach with a 6-31+G (d,p) basis set. Although all the prepared bay-substituted PDIs showed reasonable redox activity, N1 was chosen as an electrolyte dopant in dye-sensitized solar cells (DSSC) owing to its band alignment. This aided in enhanced electron lifetime and charge transfer properties, which led to an enhanced efficiency of 2.04 % while the conventional DSSC delivered only 1.84 % at 200 W m⁻² illumination. Additionally, the symmetrical supercapacitor fabricated by using Q1 as electrode material generated a high specific capacitance of 146.54 F g⁻¹. Thus, the proposed work opens avenues for the utility of bay-substituted PDI derivatives for organic electronic applications.